bignum.c - add very large number using strings.

bignum.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// basic function
char * reverse(const char* s1);
int __strlen(const char *s1);
char * ljust(const char *s1, int length, char c);
char * ltrim(const char *s1, char c);
int max(int a, int b);


// operation function
char * stradd(const char *s1, const char *s2);
char * strmpl(const char *s1, const char *s2);


int main(int argc, const char * args)
{
	printf("%s\n", stradd("3423223525626543452634587454438454552534457432453446565445556456","3428256342344523335644534523453547576845623423423451234534563456") );
	return 0;
}



// implementation operation fucntion
char * stradd(const char *s1, const char *s2)
{
	int maxLen = max(strlen(s1), strlen(s2)) + 1;
	char *a1 = ljust(reverse(s1), maxLen, '0');
	char *a2 = ljust(reverse(s2), maxLen, '0');
	// '0' --> 48, '9' --> 57
	char *r = (char*)malloc(maxLen+1 * sizeof(char));
	r[maxLen] = 0;

	int i, temp=0;
	for (i=0;i<maxLen;i++)
	{
		int v = (a1[i]-48)+(a2[i]-48)+temp;
		if(v>9) {temp = v % 10; v = v /10; } else {temp = 0; }
		r[i] = v+48;
	}
	r = ltrim(reverse(r),'0');
	free(a1);
	free(a2);
	return r;
}



// implemetation basic function
int max(int a, int b){if(a-b >=0){return a;} return b; }

char * reverse(const char *s1)
{
	int l = strlen(s1);
	char *r = (char *)malloc((l+1)*sizeof(char)); // alloc one more byte for null-ending charactor
	r[l] = 0;
	int i;
	for(i=l;i>0;i--) {r[l-i] = s1[i-1]; }
	return r;
}


char * ljust(const char *s1, int length, const char c)
{
	int l = strlen(s1);
	char *r = (char*)malloc((length+1)*sizeof(char));
	if(r==NULL){return NULL;}
	r[length] = '\0';
	int i=0;
	while(i<length)
	{
		if(i<l) {r[i] = s1[i]; }
		else {r[i] = c; }
		i++;
	}
	return r;
}

char * ltrim(const char *s1,const char c)
{
	int i = 0;
	int l = strlen(s1);
	while(s1[i] == c && i < l) {i++;}
	if(i==l) return NULL;
	char *r = (char *)malloc((l-i+1) * sizeof(char));
	r[l-i] = 0;
	memcpy(r,s1+i,l-i);
	return r;
}

void __initchars(char* s1, int len) {int i; for(i=0;i<len;i++) {s1[i] = 0;} }
int __strlen(const char *s1) {int i=0; while(s1[i] != 0) {i++; } return i; }